System for cooling a cabinet

ABSTRACT

The present disclosure relates to a cooling system comprising an active magnetic regenerator having a cold side and a hot side, a hot side heat exchanger connected to the hot side of the magnetic regenerator, one or more cold side heat exchangers, and a cold store reservoir comprising a volume of heat transfer fluid and connected between said one or more cold side heat exchangers and the cold side of the magnetic regenerator, wherein the cooling system is configured to provide a first flow cycle of said heat transfer fluid between the cold store reservoir, the magnetic regenerator and the hot side heat exchanger adapted to transfer thermal energy from the cold store reservoir to the hot side heat exchanger, and at least a second flow cycle of said heat transfer fluid between the cold store reservoir and said one or more cold side heat exchangers adapted to transfer thermal energy from said one or more cold side heat exchangers to the cold store reservoir.

The present disclosure relates to a cooling system employing an activemagnetic regenerator, a method for cooling a cabinet employing thesystem, and an associated refrigerator.

BACKGROUND OF THE INVENTION

A typical magnetic cooling system is based on an active magneticregenerator (AMR) cooling cycle comprising a magnetic regenerator formedof a magnetocaloric material, i.e. a material that heats up when placedin a magnetic field. It is known, that magnetocaloric materials can beused for heating and/or cooling purposes. Magnetic refrigerators areknown in the art, an example disclosed in US 2011/0308258, wherein anumber of magnetocaloric stages forming a magnetic refrigerator, areused to transfer thermal heat from a heat transfer fluid in a cold sideheat exchange circuit to a heat transfer fluid in a hot side heatexchange circuit.

A conventional refrigerator, such as a household refrigerator, is basedon a refrigeration cycle driven by a compressor and expansion valve inorder to deliver the required cooling load. When the refrigerator hasobtained the desired temperature, the refrigeration cycle has to delivera certain steady state load. However, in use, a refrigerator cabinet isfrequently opened in order to access the content. The interior of therefrigerator cabinet is consequently heated and in order to ensure thatthe content of the cabinet is kept cool, the cooling cycle needs todeliver a pull down load higher than the steady state load in order tocool the interior of the cabinet, preferably within a short period. Arefrigerator with a certain steady state demand may have a pull downdemand which is two to four times higher than the steady state demand.However, the refrigeration cycle of a conventional refrigerator is atleast dimensioned for the required pull down demand. Consequently, therefrigeration cycle is running in a start-stop mode during steady stateoperation.

SUMMARY OF THE INVENTION

The conventional compressor based refrigeration cycle is efficient interms of production costs but relatively inefficient in terms of energyconsumption. In contrast hereto the AMR is relatively expensive in termsof production costs but very efficient in terms of energy consumption.The high cost of manufacturing creates a significant barrier for thecommercial success of AMR based cooling systems. One purpose of thepresent invention is therefore to reduce this barrier to utilize theenergy efficiency of AMR based cooling.

A first aspect of the present disclosure therefore relates to a coolingsystem comprising an active magnetic regenerator having a cold side anda hot side, a hot side heat exchanger connected to the hot side of themagnetic regenerator, one or more cold side heat exchangers, and a coldstore reservoir comprising a volume of heat transfer fluid and connectedbetween said one or more cold side heat exchangers and the cold side ofthe magnetic regenerator, wherein the cooling system is configured toprovide a first flow cycle of said heat transfer fluid between the coldstore reservoir, the magnetic regenerator and the hot side heatexchanger adapted to transfer thermal energy from the cold storereservoir to the hot side heat exchanger, and at least a second flowcycle of said heat transfer fluid, between the cold store reservoir andsaid one or more cold side heat exchangers adapted to transfer thermalenergy from said one or more cold side heat exchangers to the cold storereservoir.

Compressor based cooling systems are dimensioned to the peak loadrequirements. However, the present inventors have realized that an AMRbased cooling system can be dimensioned to approximate the steady stateload requirements if a cold store reservoir is provided between the coldside heat exchanger and the AMR. The cold store reservoir comprises avolume of heat transfer fluid thereby significantly increasing theamount of heat transfer fluid in the cooling system and therebysignificantly increasing the pull down cooling capacity of the system.The cold store reservoir has the function of a thermal buffer in therefrigeration cycle.

A further aspect of the present disclosure relates to a method forcooling a cabinet from a first higher temperature to a second lowertemperature, the cabinet incorporating a cold side heat exchanger of thepresently disclosed cooling system, the method comprising the steps ofoperating the first flow cycle at a first steady state flow rate,operating the second flow cycle at a second flow rate higher than thefirst steady state flow rate, and monitoring the temperature in thecabinet and the temperature difference across the active magneticregenerator. This method for cooling a cabinet may be applied by meansof the herein disclosed cooling system.

A further aspect of the present disclosure relates to a refrigeratorcomprising and/or incorporating the herein disclosed cooling system.

Yet a further aspect relates to refrigeration plant comprising aplurality of refrigeration cabinets and the cooling system according toany of the preceding claims (comprising a plurality of second flowcycles) configured for cooling the plurality of refrigeration cabinets,wherein each refrigeration cabinet is connected to the cold storereservoir of the cooling system by means of one of said second flowcycles.

Thus, with the presently disclosed cooling system it is possible toreduce the load requirements for a refrigerator based on AMR which willreduce the production costs significantly. This is primarily due to thecold store reservoir which acts as a thermal buffer for the coolingsystem allowing the AMR to be dimensioned significantly below thecorresponding pull down load. An AMR typically performs best when theoutput and input temperatures on the cold side are relatively constantand are within a few degrees of each other. The output temperature fromthe heat transfer fluid exiting the cabinet may in contrast varysignificantly during pull down. As an example it may be as hot as 5° C.when initiating a pull down cycle, while in steady state it may be −5°C. The cold store reservoir buffers this temperature variation andensures that the AMR sees a much smaller variation in temperature.

DESCRIPTION OF THE DRAWINGS

The invention will in the following be described in greater detail withreference to the accompanying drawing wherein FIG. 1 is a schematic viewof one embodiment of the presently disclosed cooling system.

DETAILED DESCRIPTION OF THE INVENTION

Active magnetic regenerators are known in the art, see e.g. WO2006/074790, WO 2010/086399, Bahl et al., “Design concepts for acontinuously rotating active magnetic regenerator”, Internationaljournal of refrigeration, 34 (2011), 1792-1796, and Engelbrecht et al.,“Experimental results for a novel rotary active magnetic regenerator”,International journal of refrigeration, 35 (2012), 1498-1505. Furtherdetails of the AMR of the presently disclosed cooling system willtherefore not be described herein.

The cold store reservoir significantly increases the amount of heattransfer fluid in the cooling system. This additional volume of heattransfer fluid increases the heat capacity (and thereby the coolingcapacity) of the presently disclosed cooling system. In the steady stateduring operation of the present cooling system the heat transfer fluidis cooled to a certain minimum temperature, i.e. the volume of heattransfer fluid present in the cold store reservoir is cold. This volumeof cold heat transfer fluid can then act as a buffer in the coolingcircuit. By increasing the flow from the cold store reservoir throughthe cold side heat exchanger, i.e. the second flow cycle, it is possibleto increase the cooling load of the system for a limited period of time,i.e. a pull down can be provided without increasing the first flowcycle, i.e. without increasing the power load of the AMR. I.e. in oneembodiment the presently disclosed cooling system is configured suchthat the first flow cycle is operated independently of the second flowcycle(s). I.e. the flow rates of the first cycle and said at leastsecond flow cycle can preferably be controlled independently of eachother.

The presently disclosed cooling system is provided with a certain volumeof heat transfer fluid. The amount of heat transfer fluid depends on thespecific cooling demand of the cooling system, e.g. required steadystate load and pull-down load. A certain fraction of this volume isinside the cold store reservoir, this fraction typically depends on therequired pull-down load as will be explained below. In one embodiment atleast 50% of the total volume of heat transfer fluid in the coolingsystem is located in the cold store reservoir, or at least 60%, or atleast 70%, or at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 92%, or at least 94%, or at least 95%, or atleast 96%, or at least 97%, or at least 98%, or at least 99% of thetotal volume of heat transfer fluid in the cooling system is located inthe cold store reservoir.

In one embodiment, the presently disclosed system comprises at least afirst pump adapted to circulate heat transfer fluid between the coldstore reservoir, the AMR and the hot side heat exchanger, i.e. at leasta first pump to operate/drive the first flow cycle. The AMR ispreferably configured to be in continuous operation, i.e. constantcooling the heat transfer fluid flowing through the AMR and therebyconstantly cooling the heat transfer fluid in the cold store reservoir.This is advantageous as it enables the construction of a highlyoptimised AMR. An AMR cooling circuit performs best when the temperatureof the heat transfer fluid that enters the AMR is close to the specifiedtemperature of the heat transfer fluid that exists the AMR, preferablythis temperature difference is only a few degrees. By mixing the fluidexiting from the cold side heat exchanger into the reservoir it isensured that the temperature of the heat transfer fluid that enters thehot side of the AMR is lower than the heat transfer fluid exiting thecold side heat exchanger, thereby reducing the temperature differencebetween the hot side and the cold side of the AMR, thereby optimizingthe AMR performance. Further, the wear of the components of the AMR isreduced by minimizing the number of starts and stops. Thus, the firstpump may be configured to uphold approximate steady state conditions ofthe first flow cycle in order to optimize the operation of the AMR.

In one embodiment, the presently disclosed cooling system furthercomprises at least a second pump adapted to circulate the heat transferfluid between the cold side heat exchanger(s) and the cold storereservoir, i.e. at least a second pump to operate the second flowcycle(s). The temperature of the cold side heat exchanger may thereby becontrolled with higher precision. It is thus possible to control thetemperature of the cabinet with a higher precision. The flow rate of thefirst flow cycle may be controlled based on the temperature inside thecabinet that needs cooling. The cooling delivered to this cabinet canthen be regulated in order to cope with the demand, i.e. this at leastsecond pump may be configured to (at least indirectly) provide thepull-down load of the cooling system.

A further advantage of the presently disclosed system is that it is thesame heat transfer fluid that flows through the entire cooling system,i.e. the components of present cooling system are preferably fluidlyinterconnected. This eliminates the need for additional heat exchangersbetween the cold store reservoir and the cold side heat exchanger and/ormost importantly between the cold store reservoir and the AMR. Thissimplifies the presently disclosed cooling system greatly compared toprior art compressor based thermal reservoir systems that must use afirst heat transfer fluid at the hot end and a second fluid transferfluid at the cold end. Avoiding the use of additional heat exchangersalso reduces the energy consumption and the increases the energyefficiency of the cooling system.

The cold store reservoir is provided with at least four inlets/outletsof heat transfer fluid of possibly significantly different temperatures.Thus, there may be a temperature gradient of the heat transfer fluidinside the cold store. In a further embodiment of the cooling system atleast one mixing element is located in the cold store reservoir andconfigured to control the mixing of hot and cold heat transfer fluidinside the cold store reservoir. This may help to reduce and/or controlthis temperature gradient.

In a further embodiment the cold store reservoir is stratified toprovide for layers of heat transfer fluid. This stratification may bevertical and/or horizontal and may be one way of controlling,maintaining or reducing the temperature gradient of the heat transferfluid.

Another way to control the mixing of the heat transfer fluid in the coldstore reservoir is the location of the various inlets and outlets,utilizing the fact that the hot heat transfer fluid will tend to stay orflow towards the top of the cold store reservoir. During pull-down itmay therefore be an advantage that the inlet to the cold store reservoirfrom the cold side heat exchanger is located at a higher level than thecorresponding outlet. Correspondingly it may be an advantage that theinlet to the cold store reservoir from the active magnetic regeneratoris located at a lower level than the corresponding outlet. During steadystate operation it may be an advantage that there is a forced mixing ofthe heat transfer fluid inside the cold store reservoir.

The selection of the heat transfer fluid depends on the specificapplication of the cooling system, e.g. refrigerator or a freezer. Inone embodiment the heat transfer fluid comprises water and/or brine.Furthermore the heat transfer fluid may comprise a corrosion inhibitor.Water or brine or mixtures thereof are relatively harmless to theenvironment and has a high heat capacity. An example of a suitable brineis Zitrec S with a density of ρ=1200 kg/m³ and a specific heat of c=3.1kJ/kg*K. If water is used, corrosion inhibitors and/or anti-freezesubstance(s) may advantageously be added.

In order to estimate the load requirements of the presently disclosedcooling system, i.e. to estimate the volume of the cold store reservoirvs. the required pull-down load, it can be assumed that the AMR isoperated at constant cooling load dQ_(SS)/dt (SS=steady state). Thesteady state load dQ_(SS)/dt is the load required to keep a cabinet thatneeds cooling at a constant temperature and this load is typicallydependent on the desired cabinet temperature, the ambient temperatureand the insulation properties of the cabinet. During pull-down (PD) thecooling load is increased to dQ_(PD)/dt>dQ_(SS)/dt to cool down thecabinet. This will cause the temperature of the heat transfer fluid inthe cold store reservoir to increase. As long as the heat transfer fluidin the cold store reservoir is colder than the cabinet that needscooling (i.e. the cold cabinet), a cooling load can be extracted fromthe cold store reservoir. However, in practice it may be necessary tokeep a sufficient temperature drop across the cold side heat exchangerto maintain an adequate efficiency. It can be assumed that the cold sideheat exchanger is dimensioned such that the steady state flow ratev_(SS) is sufficient to extract the constant cooling load dQ_(SS)/dtfrom the cold cabinet with the cold store reservoir at a temperatureequal to the exit temperature of the AMR. In this case the cold storereservoir can be “bypassed” at steady state, i.e. the AMR is operatedwith the designed temperature span and cooling load. Thus, the AMR spanis not larger than otherwise; however, the steady state cooling loadwill be slightly higher due to heat losses from the cold storereservoir, since a larger part of the insulated volume is now colder. Anadded benefit of the cooling system is that the entire temperature dropdoes not need to be heat exchanged away when the cold store reservoir isrecirculated.

The volume V of additional heat transfer fluid in the cooling system,i.e. the volume of heat transfer fluid in the cold store reservoir, mustbe selected to allow for a certain temperature rise ΔT of the heattransfer fluid in the cold store reservoir to a temperature ofT_(SS)+ΔT, where ΔT typically is in the order of the temperaturedifference between the cold side inlet and outlet of the AMR. Then thepull-down load of the cooling system can be sustained for the timet_(PD) given by:

$t_{PD} = {\frac{1}{{\overset{.}{Q}}_{PD} - {\overset{.}{Q}}_{SS}}\rho \; {Vc}\; \Delta \; T}$

where ρ and c are the density and heat capacity, respectively, of theheat transfer fluid. The flow through the cold side heat exchanger musttypically be adjusted such that dQ_(PD)/dt can actually be absorbed,i.e. v_(PD)>v_(SS)=v_(AMR). For a small cooling appliance where ΔT=2 Kand V=40 liter we have that t_(PD)=90 min, i.e. the pull-down load canbe sustained for 90 minutes if a temperature rise of the heat transferfluid in the cold store reservoir of 2 degrees can be accepted, andwhere the volume of heat transfer fluid in the reservoir is 40 liter.The selection of V and ΔT is thus a balance between the cost of the AMRand the practical limitations of size of the cold store reservoir. Inorder to minimize the cost of the AMR, ΔT is typically on the order of 2degrees. In a state of the art energy efficient household refrigerator,exemplary values for the loads are, dQ_(SS)/dt=25 W and dQ_(PD)/dt=80 Wfor a small appliance. If this household refrigerator should be cooledby the presently disclosed cooling system the steady state loadrequirements of the AMR should approximate these 25 W, preferably theAMR should be dimensioned to a steady state load slightly above thesteady state load requirements, i.e. slightly more than 25 W in thiscase. Exemplary values for a large household appliance are dQ_(SS)/dt=77W and dQ_(PD)/dt=160 W. In the case of cooling a household refrigeratorthe present cooling system can be incorporated in the cabinet of therefrigerator.

Thus, in general the AMR of the presently disclosed cooling system maybe configured to approximate the steady state cooling load requirementsof the cabinet (or cabinets) that need cooling. E.g. preferably 0-20%more than a predefined dQ_(SS)/dt, or less than 20%, 18%, 16%, 15%, 14%,13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or less than 1% morethan the predefined dQ_(SS)/dt.

The cold store reservoir may further comprise an expansion volume,preferably filled with a gas such as air. E.g. the inside volume of thecold store reservoir is not completely filled with heat transfer fluidby leaving an open volume above the heat transfer fluid. The expansionvolume may be an advantage when the cooling system is not in use, forexample during transportation, where thermal expansion or contraction ofthe heat transfer fluid may vary significantly. Thus, the cooling systemmay further comprise a release valve configured to pressure-equalize thecold store reservoir. E.g. the thermal expansion of e.g. brine duringtransport to very cold places can be compensated.

As stated previously a further aspect of the present disclosure relatesto a refrigeration plant comprising a plurality of refrigerationcabinets and with the presently disclosed cooling system configured forcooling the plurality of cooling cabinets, wherein each refrigerationcabinet is connected to the cold store reservoir of the cooling systemby means of one of said second flow cycles. I.e. the AMR and the coldstore reservoir may be located centrally and be fluidly (e.g. pipelined)connected to a plurality of cold side heat exchangers, where each ofsaid cold side heat exchangers may be cooling a cabinet. In this casethe cooling system typically does not need to be incorporated in acabinet and the cold store reservoir may consequently be dimensioned tobe very large. As apparent from above this may significantly increasethe time the pull-down load can be sustained, even when the AMR isdimensioned to a temperature difference of merely 2 degrees.

Further Aspect of the Invention

One of the advantages of the presently disclosed cooling system is thatthe same heat transfer fluid can flow in the entire system, i.e. it isthe same heat transfer fluid in the first and second flow cycle(s) andin the cold store reservoir, thereby optimizing the heat transferefficiency of the system. However, a cooling system employing a coldstore reservoir can also function with the first flow cycle using afirst heat transfer fluid and the second flow cycle(s) using a secondheat transfer fluid and without a fluid connection between the coldstore reservoir and the cold side of the AMR. A further/second aspect ofthe present disclosure therefore relates to a cooling system comprising

-   -   an active magnetic regenerator having a cold side and a hot        side,    -   a hot side heat exchanger connected to the hot side of the        magnetic regenerator,    -   one or more cold side heat exchangers, and    -   a cold store reservoir comprising a volume of a second heat        transfer fluid and connected to said one or more cold side heat        exchangers,    -   a cold store heat exchanger located between the cold store        reservoir and the cold side of the magnetic regenerator,    -   wherein the cooling system is configured to provide:    -   a first flow cycle of a first heat transfer fluid between the        magnetic regenerator and the hot side heat exchanger adapted to        transfer thermal energy from the cold side of the magnetic        regenerator to the hot side heat exchanger, and    -   at least a second flow cycle of said second heat transfer fluid        between the cold store reservoir and said one or more cold side        heat exchangers adapted to transfer thermal energy from said one        or more cold side heat exchangers to the cold store reservoir.

In this second aspect the first and second heat transfer fluids are notfluidly connected and the transfer of heat between the cold storereservoir and the active magnetic regenerator is provided by means ofthe cold store heat exchanger, i.e. the cold side of the AMR is coolingthe cold store via the cold store heat exchanger. The first and secondheat transfer fluids may be the same type or different types of heattransfer fluid. AMR based cooling systems employing a cold storereservoir and a traditional heat exchanger between the cold storereservoir and the AMR have not been disclosed in the prior art. Thissolution also solves the problem of reducing the peak load requirementsof the AMR thereby significantly reducing the manufacturing costs.

As stated previously an AMR is most efficient when the output and inputtemperatures on the cold side are relatively constant, e.g. within a fewdegrees of each other. The configuration of the cold store heatexchanger, i.e. in terms of size, is advantageously optimized to ensurean adequate temperature difference between the outlet and the inlet ofthe cold side of the AMR to provide for an efficient operation of theAMR. This second aspect of the present disclosure may incorporate any ofthe features disclosed herein.

Examples

FIG. 1 shows an embodiment 1 of the presently disclosed cooling system.The cooling system 1 comprises an active magnetic regenerator 2. Aspreviously stated AMR's are known in the art and design thereof will notbe described in detail herein.

The AMR 2 is provided with four inlets/outlets: A hot side inlet 5, acold side outlet 6, a cold side inlet 7 and a hot side outlet 8. The hotside outlet 8 is connected to the inlet of a hot side heat exchanger 9,where through heat transfer fluid flows and returns to the AMR 2 throughthe hot side inlet 5. The cold side outlet 6 is connected to a coldstore reservoir 10 via the inlet 11 so that the cooled heat transferfluid exiting the AMR 2 enters the cold store reservoir 10. The coldside inlet 7 is connected to the cold store reservoir 10 via the outlet12.

The hot side heat exchanger 9 is positioned so the heat transfer fluidcan be cooled when flowing through it. In a traditional compressor basedhousehold refrigerator the hot side heat exchanger is positioned on therear of the cabinet so that it can transfer heat to the surroundings.

A first flow cycle of heat transfer fluid is constituted by the flow ofheat transfer fluid between the cold store reservoir 10, the AMR 2 andthe hot side heat exchanger 9. This first flow cycle is controlled by afirst pump 13.

A cold side heat exchanger 16 is provided in a cabinet 18 that needscooling. The cabinet 18 is insulated and can be a cabinet for aconventional household or industrial refrigerator. The cold side heatexchanger 16 is connected to the cold store reservoir 10 by means ofoutlet and inlets 14 and 15 so that heat transfer fluid can flow throughthe cold side heat exchanger 16 and return to the cold store reservoir10. A second flow cycle of heat transfer fluid is constituted by theflow of heat transfer fluid between the cold store reservoir 10 and thecold side heat exchanger 16. This second flow cycle is controlled by asecond pump 17.

By the use of the system shown in FIG. 1 the flow rate through the coldside heat exchanger 16 can then be controlled independently from theflow rate through the magnetic refrigerator 2 and hot side heatexchanger 9.

The inlet 11 is preferably positioned at a higher level than the outlet12 in order to create a temperature gradient inside the cold storereservoir 10. Correspondingly the outlet 14 from the cold storereservoir is positioned at a lower level than the inlet 15.

For example the present cooling system may be designed such that theheat transfer fluid entering the AMR 2 at inlet 7 is approx. −5° C. andthe temperature of the heat transfer fluid exiting the AMR at outlet 6is approximately −7° C. The temperature entering the cold side heatexchanger 16 from the cold store reservoir 10 will then have thetemperature of approx. −7° C. (or a little higher such as −5° C.). Thetemperature returning from the cold side heat exchanger 16 can in asteady state be as low as approximately −3° C., whereas it is higherduring pull-down, where the temperature of the heat transfer fluidentering the cold store reservoir at inlet 15 can be as high as 5° C.

In the cold store reservoir 10 shown on FIG. 1 there is an open volumeabove the heat transfer fluid. This open volume can be used tocompensate for the volume changes of the heat transfer fluid, e.g.during transportation where the temperature can vary significantlythereby functioning as expansion volume. The cold store reservoir 10 canalso be equipped with a safety valve that opens if the pressure insidethe cold store reservoir 10 gets too high and/or too low. Such a safetyvalve will hinder damages to the cooling system in case it is subjectedto critically high or low temperatures.

LIST OF REFERENCES IN DRAWINGS

-   1 cooling system-   2 AMR—active magnetic regenerator-   3 cold side of AMR-   4 hot side of AMR-   5 hot side inlet to AMR-   6 cold side outlet of AMR-   7 cold side inlet to AMR-   8 hot side outlet of AMR-   9 hot side heat exchanger-   10 cold store reservoir-   11 inlet to cold store reservoir from cold side of AMR-   12 outlet from cold store reservoir to hot side of AMR-   13 pump operating the first flow cycle-   14 outlet from cold store reservoir to cold side heat exchanger-   15 inlet to cold store reservoir from cold side heat exchanger-   16 cold side heat exchanger-   17 pump operating the second flow cycle-   18 cabinet that needs cooling

1. A cooling system comprising an active magnetic regenerator having acold side and a hot side, a hot side heat exchanger connected to the hotside of the magnetic regenerator, one or more cold side heat exchangers,and a cold store reservoir comprising a volume of heat transfer fluidand connected between said one or more cold side heat exchangers and thecold side of the magnetic regenerator, wherein the cooling system isconfigured to provide: a first flow cycle of said heat transfer fluidbetween the cold store reservoir, the magnetic regenerator and the hotside heat exchanger adapted to transfer thermal energy from the coldstore reservoir to the hot side heat exchanger, and at least a secondflow cycle of said heat transfer fluid between the cold store reservoirand said one or more cold side heat exchangers adapted to transferthermal energy from said one or more cold side heat exchangers to thecold store reservoir.
 2. The cooling system according to any of thepreceding claims, wherein the system is configured such that the firstflow cycle is operated independently of the second flow cycle(s).
 3. Thecooling system according to any of the preceding claims, wherein thesystem is configured such that the flow rate of the first flow cycle isoperated independently of the flow rate of the second flow cycle(s). 4.The cooling system according to any of the preceding claims, furthercomprising one or more pumps configured to operate the first and/or thesecond flow cycle.
 5. The cooling system according to any of thepreceding claims, further comprising a mixing element located in thecold store reservoir and configured to control the mixing of hot andcold heat transfer fluid inside the cold store reservoir.
 6. The coolingsystem according to any of the preceding claims, wherein the cold storereservoir is stratified to provide for layers of heat transfer fluid. 7.The cooling system according to any of the preceding claims, wherein theinlet to the cold store reservoir from the cold side heat exchanger islocated at a higher level than the corresponding outlet.
 8. The coolingsystem according to any of the preceding claims, wherein the inlet tothe cold store reservoir from the active magnetic regenerator is locatedat a lower level than the corresponding outlet.
 9. The cooling systemaccording to any of the preceding claims, wherein the heat transferfluid comprises water and/or brine.
 10. The cooling system according toany of the preceding claims, wherein the heat transfer fluid comprises acorrosion inhibitor.
 11. The cooling system according to any of thepreceding claims, wherein the cold store reservoir further comprises anexpansion volume, preferably filled with a gas such as air.
 12. Thecooling system according to any of the preceding claims, wherein atleast 80% of the total volume of heat transfer fluid in the coolingsystem is located in the cold store reservoir, or at least 85%, or atleast 90%, or at least 92%, or at least 94%, or at least 95%, or atleast 96%, or at least 97%, or at least 98%, or at least 99% of thetotal volume of heat transfer fluid in the cooling system is located inthe cold store reservoir.
 13. The cooling system according to any of thepreceding claims, further comprising a release valve configured topressure-equalize the cold store reservoir.
 14. A method for cooling acabinet from a first higher temperature to a second lower temperature,the cabinet incorporating a cold side heat exchanger of the coolingsystem according to any of the preceding claims, the method comprisingthe steps of: operating the first flow cycle at a first steady stateflow rate, operating the second flow cycle at a second flow rate higherthan the first steady state flow rate, and monitoring the temperature inthe cabinet and the temperature difference across the active magneticregenerator.
 15. A refrigerator comprising and/or incorporating thecooling system according to any of the preceding claims 1-13.
 16. Arefrigeration plant comprising a plurality of refrigeration cabinets andthe cooling system according to any of the preceding claims 1-13configured for cooling the plurality of refrigeration cabinets, whereineach refrigeration cabinet is connected to the cold store reservoir ofthe cooling system by means of one of said second flow cycles.